1. Field of the Invention
This invention relates to removing excess coating material which accumulates on freshly coated metal containers and more particularly relates to the removal of coating material which accumulates in the interior end areas of coated containers.
2. The Prior Art
A method of metal container manufacture in current use by the metal container industry is the two-piece can process. This process involves forming a drawn cup from a metal sheet and then deep drawing the cup into a can configuration. After the can body is completely configurated and decorated, but before the end is assembled onto the body, the interior surface of the can body is coated with a protective coating of a synthetic resin material.
It is now conventional practice in the metal container industry to apply, as the coating material, a heat hardenable resin dispersed in an aqueous medium which is sprayed into the interior walls of the container. The wet coated container is then passed through an oven in which hot air is circulated to evaporate the aqueous medium and harden the coating. In one particular method of coating two-piece cans with water dispersed heat hardenable coating materials, used by the present applicant, the open-ended can is caused to be passed in an inverted position over a reservoir of aqueous coating material which is flooded into the can interior. Excess coating material is removed to a large extent from the interior of the can by draining. However, one drawback to the use of this method, is that the viscosity and surface tension properties of the aqueous based coatings are such that after draining, there is often remains an excessive accmulation or bead of coating material on the interior edge portions of the open end of the container which are to be flanged preparatory to the application of an end closure for sealing the container by double seaming. This accumulation of coating material in the flange area is generally large enough to interfere with the double seaming operations used to the affix the closures and such interference permits leakage of the closed container.
In copending patent application Ser. No. 471,540, filed May 20, 1974, by Ihab M. Hekal, there is disclosed a method for coating the interior portions of metal containers with aqueous dispersions of heat hardenable resins wherein the coating is sprayed into the interior of the container while inverted on a reticulated belt and the wet coating is then allowed to drain. Thereafter, the container is heated to effect drying and hardening of the applied coating material. Removal of excess coating left from the draining which accumulates about the interior sidewall portions immediately adjacent the open end of the container is effected by spraying the exterior walls of the container before the heating step. Due to the difference in surface tension between the aqueous dispersion accumulated on the interior of the open end area and the water draining past the exterior of this area, a portion of the wash water draining past the exterior portion of the open end area of the container is pulled by capillary action towards the interior of the container whereby it intermixes with and dilutes the bead of accumulated resin dispersion. The so diluted resin coating dispersion is of such lowered concentration that upon drying the hardened coating is of an acceptable thickness that will not materially interfere with double seaming operations.
Although the method disclosed in Ser. No. 471,540 is effective to remove a major portion of the bead of accumulated resin, the method does not completely solve the problem encountered with accumulated coating material. It has been found, that even after the exterior wall water wash procedure disclosed in Serial No. 471,540, during the time interval after the wash and before heat hardening of the coating, the wet coating continues to drain down the interior sides of the container accumulating again at the edge portions of the container as well as in the interstices of the reticulated belt. Thereafter, when the container is heated, the coating material accumulated on the interior edge portion of the container is sometimes still present in sufficient amounts to interfere with double seaming operations and the coating material accumulated in the interstices of the belt when hardened fouls and plugs the belt causing the coating line to be shut down at frequent intervals for cleaning and removal of the accumulation of hardened coating.